1. Field of the Invention
The present invention relates to a method for designing and manufacturing tyres with the aid of a computer and an information data base.
In particular, the invention relates to a method for designing and manufacturing a tyre with given performance features, whereby the dimensions of the structural parts of the tyre are defined using a set of correlations between said structural parts, which is associated with the desired performance features of said tyre.
The invention also relates to a method for designing and manufacturing a series of tyres, whereby the dimensional characteristics of said series of tyres are automatically calculated on the basis of a reference tyre, the structure of which is automatically modified (method referred to in short as “parameterization”) by applying a set of correlations between the structural components of said reference tyre and the corresponding structural components of the tyres in said series.
The abovementioned set of correlations is used to obtain, from those of the reference tyre, the dimensional characteristics of the structural parts of said tyres in said series characterized by the fact of having, with respect to said set, a same or different size and similar or different behavioural characteristics.
The invention relates, in addition, to an integrated method for designing and manufacturing tyres, whereby the results of the different design phases are automatically converted into operating instructions for the tyre assembly machinery.
The invention also relates to a method for designing tyres, in which the design phases are at least partially determined by information or requests received, preferably in real time, from a telecommunications network (the Internet) which interfaces a processing system of the tyre manufacturer (server system) with a processing system of the client (client system).
In particular, the invention relates to a method for designing tyres, in which said information includes requests chosen by the client from within an array of options relating to dimensional and/or performance requisites of the tyre, said array being provided by the manufacturer.
2. Description of the Related Art
As is known, in the less recent tyre designing systems, a tyre is designed on the basis of a predefined series of dimensional constraints and performance characteristics which are defined depending on the clients' requirements and are processed by the design engineer, with the aid of his/her experience and technical knowledge, until it is possible to produce a production specification substantially consisting of a table which structurally describes all the constituent parts (semi-finished products) of the new tyre, defining geometrical dimensions, materials used and processing methods.
On the basis of this table, the operating unit (factory) supplies the necessary materials, machinery and equipment and, following predefined procedures, manufactures the various semi-finished products and assembles them together so as to form a rough-finished tyre. The rough-finished tyres are vulcanized in special moulds which define the external appearance of the tyre. The product then undergoes a series of checks before being authorized for sale.
The design of tyres performed with the aid of a computer has recently been developed.
The patent U.S. Pat. No. 5,710,718 describes a method for designing a tyre, comprising the following steps:                identifying a basic tyre model represented by a cross section of the said tyre including all the structural parts thereof;        selecting a plurality of physical reference parameters for evaluating the performance features of the said tyre;        selecting dimensional values defining the overall dimensions of the tyre, its cross section and the structure of the said tyre, and a plurality of physical parameters;        defining, in connection with said dimensional values, a range of maximum deviation of the structural parts of the basic model within the cross section, for the purposes of performing an optimization calculation of said parameters;        varying the value of the range of maximum deviation until one obtains, by means of an optimization calculation, an optimum value of said physical parameters which is comparable with the values of said reference values;        redesigning the tyre on the basis of the range of maximum deviation which resulted in optimization of said reference parameters.        
The patent application EP 953,834 describes a method for designing tyres, in which a basic tyre model is initially configured. A first set of variables is applied to said basic model and is used to determine conditions of the contact patch of the modelled tyre. These conditions are compared with corresponding predefined conditions of said contact patch in order to check whether the two conditions compared are convergent. If this is not so, the set of variables is incremented so as to produce new conditions for the contact patch of the modelled tyre, until values which converge towards these predefined conditions are obtained.
The set of variables considered comprises the potential wear of the tyre for which the model has been produced, the radial load exerted on the said tyre and the operating pressure.
The Applicants have observed that, in the state of the art described, the design of a new tyre comprises the step of choosing a basic tyre model, predetermining conditions or constraints representing a predefined behaviour, or predefined performance features of the new tyre, and then obtaining by means of subsequent approximations an additional tyre model which complies with the constraints predetermined at the start of the design phase, repeating a process involving modifications to and corresponding verification of the said basic model.
Recently the Applicants have developed a new method for manufacturing tyres which has eliminated the semi-finished products used in the prior art, for example the tread band, the sidewall strips, the carcass plies, the belt strips and the bead wires, just to mention a few of them. These are now replaced by only three different types of basic components which are substantially the same for any tyre and by means of which the structural parts which make up the tyre to the produced are constructed directly on a toroidal support. These three types of components are, respectively, the compound, the reinforcing cord and a rubberized fabric tape (band) consisting of a listel of compound containing two or more reinforcing cords.
The person skilled in the art, depending on the his/her different requirements and the technology available, will also be able to use a different number of basic components, for example only compounds and reinforcing cords, for example as described in the patent EP 664,232.
It is pointed out here that, in the present description, the term “reinforcing cord” refers to both individual strands and cords formed by a plurality of said strands wound together in a manner known per se.
The abovementioned toroidal support, referred to below as a drum, is a collapsible rigid support which may be extracted from the finished tyre and the radially external profile of which preferably matches the radially internal profile of the rough-finished tyre.
Except in particular cases, a tyre normally comprises several compounds of different types, for example eight compounds. The reinforcing cords may be made from textiles (usually rayon, nylon or Kevlar™) or metal, in particular with the strands consisting of HT (high tensile) steel, i.e. with a high carbon content. The bands may also be made from textiles or metal, depending on the type of cord incorporated. The Applicants prefer to use bands containing 2 to 10 cords.
The Applicants have also modified the process for assembly of the tyre, essentially eliminating the steps comprising direct movements parallel to the axis of the assembly drum, for example positioning of the bead wires, the backfolds of the ends of the carcass plies or the application of the sidewalls against the carcass, just to mention the most important ones.
This new process for assembly of the tyre is carried out by means of deposition, on the abovementioned drum, of the components designed to form the structural parts of the tyre (substantially corresponding to the parts made with the known semi-finished products according to the state of the art) using two types of movement, i.e. radial deposition, directed towards the axis of rotation of the drum, and circumferential deposition onto the surface of the drum made to rotate about its axis, or a combination of the two.
More precisely, the basic components are supplied to said drum in the form of continuous elongated parts. In a preferred embodiment, the radially deposited components are cut beforehand into portions of predefined size, while the circumferentially deposited components are cut after winding onto the drum.
These basic components have preferably a cross section with dimensions smaller than those of the structural part to be constructed and, except for the cord, preferably have a substantially rectangular shape.
More particularly, a drum is supported in cantilever fashion by the arm of a robot which is preferably of the anthropomorphic type with seven axes of rotation and which may orient the drum into any spatial position, by means of translation and/or rotation of the arm, with respect to the position for supplying of the basic component.
Typically, in this process, the band portions which form the carcass ply or plies and the belt strips are deposited with a radial movement, while the listels of compound and the reinforcing cords oriented at 0° are deposited with a spiral circumferential movement.
Preferably, the listels of compound are deposited under tension, depending on the type of composition, resulting in a stretched state of between 30% and 70% with respect to the initial length.
In particular, the carcass plies and the belt strips are constructed by depositing on the drum a circumferential succession of said pre-cut band portions by means of step-by-step rotation of the said drum. The width of the band, the angle of rotation which the drum must perform after deposition of each portion and, in the case of the belts, also the relative angle between the axis of rotation of the drum and the axis of the band portion are determined beforehand.
In a different process, according to the patent EP 664,232, radially deposited components are radially deposited on the drum with a continuous alternating movement around the torus-shaped surface of the said drum, while the latter rotates about its axis. In combination with this technology, structural parts consisting of the compound alone may be applied using a controlled-volume injection process.